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Cellular Respiration
Cellular Respiration –
AKA Respiration
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The metabolic pathways by which carbohydrates
are broken down into ATP
The formula for respiration is:
C6H12O6 + 6O2  6CO2 + 6 H2O + ATP
Respiration allows the gradual build up of ATP,
If a cell used all the potential energy in glucose
at once, too much heat would be released, and
not all the energy would be harvested.
Three Steps of Respiration
1.
Glycolysis
Yields 2 molecules of ATP
2. Citric Acid Cycle (Krebs Cycle)
Yields 2 molecules of ATP
3. Electron Transport Chain (Oxidative phosphorylation)
Yields 32 molecules of ATP
Though 36 molecules of ATP are produced, it is only 39% of
the total energy in a molecule of glucose
The Process in General
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
ATP
Substrate-level
phosphorylation
Electrons carried
via NADH and
FADH2
0%
Citric
acid
cycle
ATP
Substrate-level
phosphorylation
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
ATP
Oxidative
phosphorylation
Glycolysis
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Glyco- of or relating to glucose
Lysis- to split or burst
Changes one molecule of glucose to 2 three Carbon
molecules called pyruvate
Occurs in the cytosol (cytoplasm)
Does not require Oxygen
Glycolysis
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Glucose  2 pyruvate
2 NAD  2 NADH
2 ADP
4 ATP
2 ATP 
Net gain of 2 ATP molecules (top=input, bottom= outputs)
2 ATP  2ADP
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P + 2NAD2NADH
GlucoseFructosePGALPGAPEPpyruvate
2 ATP
H2O
2 ATP
Glycolysis
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When Oxygen is present, glucose / pyruvate can
be broken down further in a process called the
Krebs cycle.
However, when Oxygen is not present pyruvate
can be broken down through the process of
fermentation.
Aerobic respiration- respiration with Oxygen
Anaerobic respiration- respiration with out
Oxygen
The Evolutionary Significance of
Glycolysis
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Glycolysis occurs in nearly all organisms
Glycolysis probably evolved in ancient
prokaryotes before there was oxygen in the
atmosphere
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Fermentation
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Glycolysis + the reduction of pyruvate to lactic
acid, alcohol, or CO2
Fermentation is inefficient. But when O2 is not
present it is better than nothing.
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Glycolysis yields 2 ATP, fermentation yields 2 more
Fermentation yields only 14.6 Kcal of a possible
686Kcal from 1 molecule of glucose that is
about 2.1% efficient.
Fermentation
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In yeast produces alcohol and CO2  death
In humans produces lactic Acid  soreness
In athletes :
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because of training more mitochondria are produced in
the muscle cells.
b/c of higher # of mito., they utilize more O2 and can
produce more ATP (less O2 wasted)
Means less Oxygen debt or deficit
Less fermentation
Less soreness
Types of Fermentation
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Fermentation consists of glycolysis plus reactions
that regenerate NAD+, which can be reused by
glycolysis
Two common types are alcohol fermentation and
lactic acid fermentation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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In alcohol fermentation, pyruvate is converted to
ethanol in two steps, with the first releasing CO2
Alcohol fermentation by yeast is used in brewing,
winemaking, and baking
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 9-18
2 ADP + 2 Pi
Glucose
2 ATP
Glycolysis
2 Pyruvate
2
NAD+
2
+ NADH
2 H+
2 CO2
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 Pi
Glucose
2 ATP
Glycolysis
2
NAD+
2 Lactate
(b) Lactic acid fermentation
2
+ NADH
2 H+
2 Pyruvate
Fig. 9-18a
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 Ethanol
(a) Alcohol fermentation
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
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In lactic acid fermentation, pyruvate is reduced
to NADH, forming lactate as an end product, with
no release of CO2
Lactic acid fermentation by some fungi and
bacteria is used to make cheese and yogurt
Human muscle cells use lactic acid fermentation to
generate ATP when O2 is scarce
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 9-18b
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 NAD+
2 Lactate
(b) Lactic acid fermentation
2 NADH
+ 2 H+
2 Pyruvate
Fermentation and Aerobic Respiration
Compared
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Both processes use glycolysis to oxidize glucose
and other organic fuels to pyruvate
The processes have different final electron
acceptors: an organic molecule (such as pyruvate
or acetaldehyde) in fermentation and O2 in cellular
respiration
Cellular respiration produces 38 ATP per glucose
molecule; fermentation produces 2 ATP per
glucose molecule
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Obligate anaerobes carry out fermentation or
anaerobic respiration and cannot survive in the
presence of O2
Yeast and many bacteria are facultative
anaerobes, meaning that they can survive using
either fermentation or cellular respiration
In a facultative anaerobe, pyruvate is a fork in the
metabolic road that leads to two alternative
catabolic routes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 9-19
Glucose
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
Aerobic Respiration
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Occurs when Oxygen is present
Produces 36 ATP molecules
Begins after glycolysis
The Transition reaction connects glycolysis to
the Aerobic pathways (Krebs cycle & Electron
transport chain).
Transition Reactions
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Connects glycolysis to the Krebs cycle
The pyruvate from glycolysis is converted to a 2
Carbon compound called an acetyl group.
The acetyl group is attached to Coenzyme A
The resulting complex is Acetyl Coenzyme A
(Acetyl CoA)
Coenzyme- protein that acts as a carrier
molecule in biochemical processes.
This process releases CO2
Transition Reaction
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Occurs twice for each glucose molecule
Occurs in the matrix of the mitochondria
2 NAD  2 NADH + H-
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2 pyruvate + 2 CoA  2 Acetyl CoA + 2 CO2
Mitochondrial structure
Cristae - location of the electron transport chain
 Cytosol – location of glycolysis
 Matrix- location of the transition reactions and
the Krebs cycle.
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Fig. 9-10
CYTOSOL
MITOCHONDRION
NAD+
NADH + H+
2
1
Pyruvate
Transport protein
3
CO2
Coenzyme A
Acetyl CoA
Krebs Cycle
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The products of the Transition RXN are the reactants of
the Krebs Cycle.
The Krebs Cycle is also known as the Citric Acid Cycle.
Citrate is the first metabolite produced in the Krebs
Cycle.
During the Krebs Cycle:
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the acetyl group on Acetyl CoA is oxidized to CO2.
Some of the electrons (H ions) are accepted by NAD,
but 1 is picked up by another electron carrier, FAD.
Some ATP is produced by phosphorylation like in glycolysis.
The Krebs Cycle turns twice for each original molecule
of glucose.
Krebs Cycle
Inputs
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2 acetyl groups
2 ADP + 2 P
6 NAD
2 FAD
Outputs
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4 CO2
2 ATP
6 NADH
2FADH2
See Figure 9.7
Acetyl CoA
CoA—SH
NADH
H2O
NAD+
Oxaloacetate
Isocitrate
Malate
Citrate
NAD+
Citric
acid
cycle
NADH
CO2
H2O
Fumarate
CoA—SH
-Ketoglutarate
CoA—SH
FADH2
NAD+
FAD
Succinate
NADH
P
Succinyl
CoA
ADP
ATP
CO2
Fig. 9-7
Substrate-level phosphorylation:
• Use of an enzyme to produce ATP and
another product
+
ADP
P
Substrate
ATP
Product
The Electron Transport Chain
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Located in the cristae
Series of electron carriers that pass an electron from
one to another.
The electrons in the electron transport chain come
from NADH and FADH2 in the Krebs Cycle
Drives the process that generates most of the ATP .
The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
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Electrons are transferred from NADH or FADH2
to the electron transport chain
Electrons are passed through a number of
proteins including cytochromes (each with an
iron atom) to O2
The electron transport chain generates no ATP
The chain’s function is to break the large freeenergy drop from food to O2 into smaller steps
that release energy in manageable amounts
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 9-13
NADH
50
2 e–
NAD+
FADH2
2 e–
40
FM
N

FAD
Multiprotein
complexes
FAD
Fe•S
Fe•S

Q

Cyt b
30
Fe•S
Cyt c1
I
V
Cyt c
Cyt a
20
10
0
Cyt a3
2 e–
(from NADH
or FADH2)
2 H+ + 1/2 O2
H2O
Chemiosmosis: The Energy-Coupling
Mechanism
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Electron transfer in the electron transport chain causes
proteins to pump H+ from the mitochondrial matrix to
the intermembrane space
H+ then moves back across the membrane, passing
through channels in ATP synthase
ATP synthase uses the exergonic flow of H+ to drive
phosphorylation of ATP
This is an example of chemiosmosis, the use of energy
in a H+ gradient to drive cellular work
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The energy stored in a H+ gradient across a
membrane couples the redox reactions of the
electron transport chain to ATP synthesis
The H+ gradient is referred to as a proton-motive
force, emphasizing its capacity to do work
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Fig. 9-14
INTERMEMBRANE SPACE
H+
Stator
Rotor
Internal
rod
Catalytic
knob
ADP
+
P
i
ATP
MITOCHONDRIAL MATRIX
Oxidative Phosphorylation
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The process by which ATP production is tied to
an electron transport system that uses Oxygen as
a final electron receptor.
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After Oxygen accepts the electron it binds with
Hydrogen from the matrix and form H2O
Figure 9.8
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Complexes of the Electron
Transport Chain
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NADH dehydrogenase - causes the oxidation of
NADH.
Cytochrome b-c complex - the complex which
receives electrons and pumps H ions into the
inter-membrane space.
Cytochrome oxidase complex - receives
electrons and passes them to oxygen.
Electron Transport Chain
The Process in General
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
0%
Glycolysis
Glucose
Pyruvate
ATP
Substrate-level
phosphorylation
Citric
acid
cycle
ATP
Substrate-level
phosphorylation
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
ATP
Oxidative
phosphorylation
The process with details
Electron shuttles
span membrane
CYTOSOL
2 NADH
2 NADH
or
2 FADH2
2 NADH
Glycolysis
Glucose
MITOCHONDRION
2
Pyruvate
2
Acetyl
CoA
+ 2 ATP
6 NADH
Citric
acid
cycle
+ 2 ATP
Maximum per glucose:
About
36 or 38 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
Concept 9.6: Glycolysis and the
citric acid cycle connect to many
other metabolic pathways
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Gycolysis and the citric acid cycle are major
intersections to various catabolic and anabolic
pathways
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Versatility of Catabolism
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Catabolic pathways funnel electrons from many
kinds of organic molecules into cellular respiration
Glycolysis accepts a wide range of carbohydrates
Proteins must be digested to amino acids; amino
groups can feed glycolysis or the citric acid cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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Fats are digested to glycerol (used in glycolysis)
and fatty acids (used in generating acetyl CoA)
Fatty acids are broken down by beta oxidation
and yield acetyl CoA
An oxidized gram of fat produces more than twice
as much ATP as an oxidized gram of carbohydrate
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 9-20
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde-3-
NH
P
Pyruvate
3
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Fatty
acids
Regulation of Cellular Respiration
via Feedback Mechanisms
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Feedback inhibition is the most common
mechanism for control
If ATP concentration begins to drop, respiration
speeds up; when there is plenty of ATP,
respiration slows down
Control of catabolism is based mainly on
regulating the activity of enzymes at strategic
points in the catabolic pathway
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings